Models of Accommodation. In: Hung GK, Ciuffreda KJ, editors. Models of the Visual System. Boston: Springer US; 2002. pp. 287-339. [DOI: 10.1007/978-1-4757-5865-8_8]

Effects of age on dynamic accommodation

Visual accommodation plays a critical role in one's visual perception and activities of daily living. Age-related accommodation loss poses an increased risk to older adults' safety and independence. Although extensive effort has been made towards understanding the effect of age on steady-state accommodation, dynamic aspects of accommodation is still unknown. A study was therefore conducted to investigate age-related dynamic accommodative characteristics utilising a modified autorefractor. Ten individuals from each of three age groups (i.e. younger group: 20 to 29 years old; middle-aged group: 40 to 49 years old; older group: 60 to 69 years old) were recruited and their dynamic accommodation responses were examined. The laboratory experiment was designed to assess dynamic accommodation associated with an abrupt change from a constant far target (400 cm, 50 cd/m(2)) to a near target (70 cm, 100 cd/m(2) or 20 cd/m(2)), which aimed to simulate car dashboard reading behaviour while driving. The results of the study indicated that age and target intensity both had a significant impact on dynamic accommodation. These effects were attributed to both the age-related physiological limitation of the eye as well as to central neural processing delay. A method of measuring dynamic accommodation and the implications of the study are discussed. STATEMENT OF RELEVANCE: The results of the study indicate that age and target intensity both have a significant impact on dynamic accommodation. These effects are attributed to age-related physiological limitation of the eye as well as central neural processing delay and to decreased sensitivity of the cone photoreceptors. To enhance the visual performance of the ageing population involving dynamic accommodation, target distance and target light intensity should be carefully evaluated to facilitate effective viewing.

The effect of apparent depth in pictorial images on accommodation

The purpose of this study was to investigate the effect of the apparent depth of pictorial images on accommodation. Steady-state accommodation was assessed objectively while viewing eight pictorial stimuli containing varying degrees of monocular cues to depth. Sixteen young adult subjects were tested monocularly with accommodation either in the closed-loop or open-loop mode. Pictorial depth cues significantly influenced the mean level of accommodation under some of the open-loop conditions in which blur feedback was rendered ineffective. For nearly all stimuli and viewing modes, the mean accommodative responses were biased in the perceptually-appropriate direction, but they were larger in the open-loop condition. Apparent depth cues did not significantly affect accommodation under closed-loop viewing conditions, presumably because blur feedback markedly dampened any perceptually-driven influences. Consistent with current models of accommodation, and several earlier studies, perceptually-based accommodation had only a secondary effect on the overall accommodative response level under naturalistic viewing conditions, with blur dominating.